# \textit{Ab Initio} Study of the Magnetic Behavior of Metal Hydrides: A Comparison with the Slater-Pauling Curve

## TL;DR

This study uses Density Functional Theory to analyze how hydrogen concentration affects the magnetic properties of Fe, Co, and Ni hydrides, revealing their behavior aligns with the Slater-Pauling curve and identifying volume expansion and electron addition as key factors.

## Contribution

It provides a detailed ab initio analysis of magnetic moments in metal hydrides and compares the results with the Slater-Pauling curve, highlighting the effects of hydrogenation on magnetism.

## Key findings

- Magnetic moments in CoH$_{x}$ and NiH$_{x}$ decrease with hydrogen concentration.
- In FeH$_{x}$, magnetic moments vary depending on hydrogen content.
- Magnetic behavior of metal hydrides aligns with the Slater-Pauling curve.

## Abstract

We investigated the magnetic behavior of metal hydrides FeH$_{x}$, CoH$_{x}$ and NiH$_{x}$ for several concentrations of hydrogen ($x$) by using Density Functional Theory calculations. Several structural phases of the metallic host: bcc ($\alpha$), fcc ($\gamma$), hcp ($\varepsilon$), dhcp ($\varepsilon'$), tetragonal structure for FeH$_{x}$ and $\varepsilon$-$\gamma$ phases for CoH$_{x}$, were studied. We found that for CoH$_{x}$ and NiH$_{x}$ the magnetic moment ($m$) decreases regardless the concentration $x$. However, for FeH$_{x}$ systems, $m$ increases or decreases depending on the variation in $x$. In order to find a general trend for these changes of $m$ in magnetic metal hydrides, we compare our results with the Slater-Pauling curve for ferromagnetic metallic binary alloys. It is found that the $m$ of metal hydrides made of Fe, Co and Ni fits the shape of the Slater-Pauling curve as a function of $x$. Our results indicate that there are two main effects that determine the $m$ value due to hydrogenation: an increase of volume causes $m$ to increase, and the addition of an extra electron to the metal always causes it to decrease. We discuss these behaviors in detail.